A PRECIPITATOR FOR AN ELECTROSTATIC FILTER

Abstract: In an electrostatic precipitator for an electrostatic filter at least one group (11 and/or 12) of electrode or plate elements of like polarity are made of or coated with a semiconducting or dissipative material, and the electrode elements of at least one group (12) comprise or are associated with a screen (16) of an insulating material at the edge thereof which is directed against the stream (A) of air through the precipitator.

Description: A precipitator for an electrostatic filter This invention relates to a precipitator for a two-stage electrostatic filter. WO 93/16807 discloses a two-stage electrostatic filter which comprises an ionizer and a capacitor or electrostatic precipitator (collector) positioned downstream of the ion¬ izer. Advantageously, the electrode elements of the precipi¬ tator, which in the illustrated embodiment are flat plates but may have different shapes in other embodiments, are made of a material that may be designated as highly resistive or antistatic (so-called dissipative material) . With such a material a substantial improvement can be achieved, because the voltage that can be produced between adjacent electrode elements is self-regulating and can reach higher values than in the customary electrostatic filters having electrode ele¬ ments made of a material of low resistivity, such as alumin¬ ium, and having a galvanic connection to the voltage source. In the embodiment disclosed in the above-mentioned pub¬ lication, the plates preferably are charged by the ion cur- rent from the corona electrode of the ionizer, and the volt¬ age between them is stabilized because the electrode elements have field-concentrating formations, which may take the shape of, for example, sharp edges or other pointed parts of the electrode elements. The present invention advantageously can be embodied in two-stage electrostatic filters of the kind disclosed in the above-mentioned publication, but it is not limited to use in filters of that kind. For example, the charged particles by means of which the precipitation of dust on the electrode elements is brought about need not necessarily be produced in an ionizer of the type disclosed, but may be produced and carried to and through the precipitator in any suitable man¬ ner. Moreover, it is not necessary that the electrode ele¬ ments be charged by the air ions produced in the ionizer. Instead, the required voltage between adjacent electrode elements may be maintained by a connection of the electrode elements to a high-voltage source, preferably a very highly resistive connection. An object of the invention is to provide a high, and yet stable, voltage, i.e. a high threshold voltage, with narrow air gaps between adjacent electrode or plate elements of the precipitator, so that the precipitator may be used in applica- tions in which the precipitator has to meet high stringent demands in respect of precipitation capability. According to the invention, this object is attained by using a highly resistive, antistatic or almost antistatic (dissipative) material of, or coating on, the electrode ele- ments of the precipitator and at the same time avoiding field concentrations, especially at those edges of the electrode elements which are at the upstream end of the electrode ele¬ ments and, consequently, confront the stream of air that carries the charged particles to be precipitated on the elec- trode elements. According to the invention, this can be accomplished by providing the electrode element edges in question with a screen made of a non-conducting, insulating material. This screen need not necessarily be applied to the edges, meaning that it need not be physically connected with the edges, but may be slightly spaced from them; it is sufficient that the screen is constructed and positioned such that it electrosta¬ tically screens the edges from the electric field. The screening may be provided by making the electrode elements from an insulating material and coating them with a semiconducting or antistatic material such that their edges are left insulated (uncoated) so that only the electrode ele¬ ment surface inwardly (downstream) of the edges is semicon¬ ducting or antistatic. The same effect may be achieved if the electrode ele¬ ments are made from a semiconducting or antistatic material and the edges thereof are coated with an insulating, non-con¬ ducting material. Advantageously, the first-mentioned way of providing the screening may be used in cases in which a cellulose material, such as paper or cardboard, is used for the electrode ele¬ ments and the precipitator is to operate in a dry and warm environment. An example of such cases is precipitators of electrostatic filters for vacuum cleaners. In such cases, the excellent natural semiconducting or antistatic properties of the cellulose material may be lost after some time of opera¬ tion because of the heating of the air that occurs in the vacuum cleaner, so that the material becomes comparable to an insulating material. In the preferred embodiment of the present invention, the electrode elements may advantageously be charged by air ions supplied from an ion current generated by a corona elec- trode positioned upstream of the precipitator in accordance with the disclosure of the above-mentioned publication. To this end, the electrode elements to be charged in this manner should project in the upstream direction beyond the electrode elements of a different polarity - preferably, the last-mentioned electrode elements are grounded and for the sake of simplicity will be referred to hereinafter as the grounded electrode elements whereas the first-mentioned elec¬ trode elements will be referred to as the charged electrode elements - and they should also be screened in the above- explained manner so that field-concentrating formations at the edges are screened. If not screened, these formations would limit the voltage because of discharges to the grounded electrode elements. Similar considerations apply to the trailing or down- stream end of the grounded electrode elements. In the pre¬ ferred embodiment the grounded electrode elements extend in the downstream direction beyond the charged electrode ele¬ ments. The trailing edge of the grounded electrode elements, which thus protrudes in the downstream direction, may advan- tageously also be antistatic or semiconducting so that it can readily be connected to ground. In the preferred embodiment of the present invention, the electrode elements are insulated from one another. The insulation may be arranged such that it covers the electrode element edges extending in the direction of air flow so that these edges are also screened from the electrical field. As is apparent from this description, the invention com¬ prises screening of the field-concentrating formations which • <τ , W co h υi -r < • * * > m * • » m O At their downstream edges, the grounded plates 12 are provided with a conductive coating 18 forming an electrical connection between the body of the plates and the contact strip 14.

Claims: W co υ H PL. c r- I • •sr O

Inventors: LORETH ANDRZEJ, TOEROEK VILMOS, LORETH, ANDRZEJ, TOEROEK, VILMOS
Applicants: LORETH ANDRZEJ, TL VENT AB, TOEROEK VILMOS, LORETH, ANDRZEJ, TL-VENT AB, TOEROEK, VILMOS
Application year: 1994
Main classification: B03C3
IPC codes: B03C3